Revegetation of lagoon ash using the legume species Acacia auriculiformis and Leucaena leucocephala

A greenhouse study was conducted to evaluate the potential use of two legum e species, Acacia auriculiformis and Leucaena leucocephala for growth on am eliorated lagoon ash with or without nitrogen (N-2)-fixing bacteria inocula tion. Even though amendments of 30% (w/w) vermiculite or with sewage sludge compost were added to improve the chemical and physical limitations of lag oon ash, significant suppressions in biomass and plant nutrient content wer e found with ameliorated lagoon ash in comparison to an agricultural soil. The high proportion of clay-sized (< 53 mu m) ash particles limited root gr owth. In addition, heavy metal toxicity was a possible factor contributing to poor seedling growth. Higher plant productivity resulted from the sewage sludge compost-amended lagoon ash than with vermiculite due to a greater c ontribution of plant nutrients in the compost. Nodulation was inhibited in ameliorated lagoon ash but not in agricultural soil. High pH and electrical conductivity and elevated toxic metals may be important parameters that li mit bacterial activity. Both species showed potential to establish on amend ed lagoon ash, with Acacia auriculiformis being the best adapted. (C) 2000 Elsevier Science Ltd. All rights reserved.